It happens, as a consequence of a disease or an accident, that people lose several teeth in one or both jaws. These teeth must be replaced by artificial teeth in the form of a denture. The denture can either be detachable or anchored in fixtures that have been inserted in the jawbone by surgical operation.
Applicant's earlier Application WO 90/05499 discloses a method of making a device for supporting artificial teeth, which below is referred to as bridge structure. The bridge structure is adapted to be secured to anchoring elements, which are embedded entirely or partly in the jawbone. The anchoring elements may be fixtures or fixtures with extension members fixed thereto. The bridge structure is moulded in one piece according to a model which is prepared individually for each patient. It has a tubular connector for each anchoring element to which the bridge structure is to be fixed, and a tooth-supporting means which extends between the connectors and which in the completed denture supports the artificial teeth. When moulding the bridge structure, dimensional changes occur, which make the bridge structure not perfectly fit the anchoring elements.
According to the above-mentioned WO 90/05499, this problem can be solved in the following manner. Extension members are screwed into the anchoring elements in a model of the patient's jaw. After that one or more planes through the extension members are determined. The planes are determined such that the bridge structure is positioned on a desired level in relation to the jawbone. Then the extension members are shortened such that their end surfaces are located in the predetermined planes. Finally, the end surfaces of the connectors of the bridge structure are treated such that the connectors are in the predetermined planes when the bridge structure is being secured to the anchoring elements.
It is important for the extension members and the treatment of the end surfaces of the connectors to be made with great accuracy, such that the end surface of an extension member and the corresponding end surface of a connector will really be in a common plane. The better agreement with the common plane, the less stresses arise when the bridge construction is secured to the anchoring elements.
WO 99/05499 describes that the planes can be made by the model with the extension members being secured in an artificial jaw joint and by one or more desired planes through the extension members being marked. Then the model with the extension members is passed on to a spark erosion machine, in which the extension members are cut in the indicated planes. The connectors are then cut in a corresponding manner in the spark erosion machine. This method functions best when all extension members and all connectors are cut in one and the same plane. If one wants to cut the extension members at different heights, it will be necessary to perform accurate manual measuring and marking of the planes and accurate setting of the spark erosion machine.